Direct observation of the line mixing in the oxygen B band
We present the results of CRDS investigation of two pairs of overlapping transitions in the oxygen B-band head.
Measurements were performed with frequency-stabilized cavity ring-down spectrometer (FS-CRDS) referenced to an optical frequency comb. We exploited the new setup of the spectrometer in dual-polarization configuration which allows for the probe beam to be switched and tuned independently from the PDH lock beam, similarly as described in Ref. . The R19R19, R21R21, R19Q20, and R21Q22 lines were measured in the pressure range up to 32 Torr with actively stabilized temperature to 296 K. Recorded spectra were analyzed using the multispectrum fitting technique in order to reduce the numerical correlations between fitted line-shape parameters [2, 3]. The line-shape models fitted to the spectra included speed dependence (speed-dependent Voigt profile, SDVP), speed dependence and Dicke narrowing (speed-dependent Nelkin-Ghatak profile, SDNGP) and line mixing (SDVP + LM, SDNGP + LM) . Line positions, line intensities, pressure coefficients for broadening, shifting and narrowing were determined with the quality-of-the-fit QF (the ratio of the peak absorption signal to the standard deviation of the fit residuals ) parameter exceeding 22000 for the best fits. Although the pressure was as low as 0.04 of atm we were able to determine the first-order O2-O2 line mixing coefficients and explain some questions concerning line shifts and speed-dependent parameters . Incorporation of the line mixing in the oxygen B band modeling is also crucial in the collision-induced absorption (CIA) determination . Results for LM parameters were compared with available calculated data .
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